1. Field of the Invention
The subject invention relates to a hypodermic syringe having activation structures which enables an initial piercing of a barrier in the syringe and subsequent removal of a needle shield in response to a continuous motion of the activation assembly.
2. Description of the Prior Art
A hypodermic syringe has a syringe barrel with an open proximal end and an opposed distal end. A cylindrical wall extends between the ends of the barrel to define a fluid-receiving chamber. The distal end of the syringe barrel includes a passage for fluid communication with the chamber. A needle cannula may be mounted to the distal end of the barrel and a needle shield may be removably mounted over the needle cannula to protect the needle before use. The hypodermic syringe also has a plunger in sliding fluid-tight engagement with the cylindrical wall of the chamber. Movement of the plunger toward the distal end of the syringe barrel urges fluid in the chamber toward the needle cannula.
Many hypodermic syringes are pre-filled with a fluid that must be isolated in the syringe barrel to prevent contamination of the fluid. The prior art includes hypodermic syringes that achieve this isolation with a barrier between the chamber and the needle cannula. These prior art hypodermic syringes may include a needle cannula with a proximally facing point for piercing the barrier and enabling fluid in the chamber to communicate with the needle cannula. Some prior art hypodermic syringes use the needle shield for moving the needle cannula in a proximal direction to pierce the barrier. Thus, a health care worker may urge a prior art needle shield in a proximal direction to cause the proximally facing point of the needle cannula to pierce the barrier in the syringe barrel.
One prior art hypodermic syringe with a needle shield that can initially move in an axial direction for piercing the barrier is shown in U.S. Pat. No. 4,639,250.
The above-described prior art requires a first action by a health care worker to pierce the barrier, followed by a separate and distinct action to remove the needle shield.